According to EP B1 01 74 039, the winding speed at which yarn is wound onto the yarn storage surface is adjusted in accordance with the difference between a predetermined desired value and an actual value of the number of yarn windings supported on the storage surface, and in such a manner, that this difference varies within a limited range between a positive value and a negative value. The desired value corresponds to the number of yarn windings required for satisfying a mean consumption. Although in this case a low winding speed in combination with a low mean consumption results in the creation of a suitably adapted yarn supply, a yarn supply of the same magnitude is not required at higher winding speeds. In the case of a state of equilibrium between the winding speed and the mean consumption, an increase of the yarn consumption at higher winding speeds results in that the yarn supply is replenished at a faster rate than in the case of lower winding speeds, due to the high-speed operation of the winding drive mechanism. An excessive yarn supply is undesirable, however, particularly in the higher winding speed range, because the danger of windings being wound upon one another is increased, and because the winding speed during the replenishment of the yarn supply to an unnecessary size tends to become excessive. Also during the replenishment of the yarn supply to an unnecessary size, the adaptation of the winding speed to a new state of equilibrium after a change of the consumption takes a long time, and excessive speed results in an undesirable increase of the mechanical stress acting on the yarn, involving the danger of yarn breakage, particularly at the yarn supply side. Also the size of the yarn supply can be further and excessively increased, proceeding from the already unnecessarily great yarn supply, in the case of a delay caused by a decrease of the yarn consumption. The great number of windings in the excessively great yarn supply hampers the advance of the yarn supply. The temporarily excessive speed and the mostly excessive yarn supply also result in an unnecessary energy consumption.
It is an object of the invention to provide a method and a yarn storage and feeder device to thereby ensure the presence of a yarn supply of optimum magnitude on the storage surface.
These objects are attained according to the invention by a method and device having the characteristics set forth below.
Both in the case of the method and of the device, the proposed object is simply attained by the consideration that, in the case of higher winding speeds, the winding drive mechanism is capable in response to an increase of consumption of replenishing the yarn supply to the necessary size more rapidly than in the case of lower winding speeds, and that without the danger of the yarn supply being completely depleted, so that the yarn supply can be smaller at higher winding speeds than at lower winding speeds. This is brought about by respective changes of the desired value. In the case of a decrease of consumption, the change of the desired value prevents the size of the yarn supply from being undesirably increased, the selected desired value being effective to adjust the yarn supply to the minimum size required for the reduced consumption. The manner in or the law by which the desired value is varied is at least in part dependent on the capacity of the winding drive mechanism, which may be represented by a known characteristic curve specific to the respective device. This characteristic curve may for instance be the acceleration curve of the winding drive mechanism. The consumption, or the characteristic of the consumption, respectively, is likewise of importance with regard to the variation of the desired value. It is to be preceeded from the assumption, however, that the yarn storage and feeding device is a priori matched to the consumer in such a manner that a reliable yarn supply is ensured under any operative conditions to be expected. The variation of the desired value is of particular importance not only during normal operation, but also in the starting phase and in the run-out phase down to the stopped condition, because under these circumstances the desired value plays an important role by preventing the occurrence of excessive speeds, and the formation of an excessive yarn supply in the run-out phase, respectively. The reduction of the yarn supply to its optimum size for any consumption rate results in various advantages. In the first place, the adjusted size of the yarn supply reduces the danger of windings being wound upon one another. The drag forces opposing the advance of the yarn supply are considerably reduced. Furthermore there results a reduced maximum speed of the winding drive mechanism, because in the case of an increased consumption rate the winding speed will no longer become excessive to thereby create the unnecessarily great yarn supply for this high winding speed. By the avoidance of such excessive speeds the mechanical stress acting on the yarn, particularly on the supply side, is reduced, with the resultant reduction of the danger of yarn breakage at this location. The formerly unavoidable swinging adjustment of the winding speed towards equilibrium with the consumption rate is eliminated, because the winding speed is adjusted in harmony to the consumption rate with the aid of the desired values. The elimination of the swinging adjustment results in the applicable state of equilibrium being attained very quickly. After the winding speed has been reduced in response to the consumption rate, the size of the yarn supply is immediately matched to the new consumption rate, because the winding speed is matched to the consumption rate without any noticeable swinging adjustment as a result of the variation of the desired value.
In summary, the method according to the invention and the construction of the yarn storage and feeding device result in an improved quality of the yarn feeding process with improved energy husbandry and reduced danger of malfunction.
One embodiment of the method permits the optimum small size of the yarn supply to be obtained in each case in a simple manner. The higher the winding speed at a given state of equilibrium, the smaller is the yarn supply. Since the variation of the desired value is brought about in an automatic manner, there is no need for external intervention.
Another provision takes into account that a relatively great yarn supply is required at lower winding speeds, because in the case of an increase of the consumption rate the winding drive mechanism is only capable of replenishing the supply at a slow rate.
A starting number can be established in view of the fact that the winding drive mechanism, proceeding from the stopped condition, requires a relatively long time for building the yarn supply up to the necessary size in the case of an increase of the consumption rate. The starting number may thus correspond to the desired value for the slowest winding speed (standstill). It is also conceivable, however, to select a higher starting number, and to commence the adjustment of the winding speed in accordance with the variation of the desired value only after a predetermined winding speed or a state of equilibrium has been attained. The starting number is also required for the initial establishment of the yarn supply. Under the assumption of a known and substantially constant mean consumption rate, the desired objective can also be attained with at least one alteration of the desired value, i.e. by applying to the control unit at least one desired value different from the starting number and matched to the known mean consumption rate, to thereby ensure that the yarn supply at this mean consumption rate is of optimum smallness, i.e. smaller than during the start-up phase. The respective desired value, or rather the alteration of the desired value, preferably comes into effect with regard to the control function when the state of equilibrium has been attained after the start-up phase of the drive mechanism. In this manner it is possible to suppress a swinging adjustment phase, because this adjustment of the winding speed is carried out soon after leaving the starting number by matching the winding speed to the desired value.
When the control of the winding speed according to the desired values is effective to always ensure the optimum smallness of the yarn supply, and the winding speed control process proceeds in a harmonic manner, the result is a limitation not only of the mechanical stresses acting on the yarn, but also the variations of the yarn tension on the supply side.
The characteristic acceleration curve of the winding drive mechanism is a very useful point of departure for determining the different desired values. This is because the speed at which the yarn supply is replenished or diminished is to a large extent dependent on the acceleration and/or deceleration response of the winding drive mechanism. This proceeds from the assumption that the actual diameter of the storage surface, which may also be adjustable, or the yarn quality are only of secondary importance.
The desired value may be determined in accordance with the known mean consumption rate, i.e. the desired value is either calculated or empirically determined and applied to the control unit for use in its operation.
One manner of conducting the method permits a very fine control function to be achieved. The frequency at which the information comparison is repeated depends on the actually given operating conditions. This frequency may also be selected to be higher or lower, for instance by means of an adjustable clock generator for the control unit.
Of particular advantage in this context is the performance of the method using a closed control loop, because the closed control loop, which is dominated by the desired values acting as reference values, permits a very fine control function to be achieved.
In the yarn storage and feeding device according to the invention, the speed control function of the control unit is influenced by a reference value memory so as to establish and maintain the optimum smallness of the yarn supply at any winding speed value. Since the operation of the control unit is governed by the desired values, an increase of the winding speed to excessive values in response to an increase of the consumption rate is avoided in the same manner as an undesirable increase of the size of the yarn supply in response to a reduced consumption rate. The mechanical stresses acting on the yarn are thus maintained as small as possible. The optimum smallness of the yarn supply in each winding speed range notwithstanding, the complete exhaustion of the yarn supply in response to an increase of the consumption rate is reliably avoided.
The acceleration curve of the winding drive mechanism is a known reference line and as such is useful for calculating or determining the desired values.
A further advantageous embodiment includes a microprocessor in the control unit and detector means acting to supply the control unit with informations relating to the number of windings as wound and the number of windings as consumed, and further relating to at least one desired value. The microprocessor is suitably informed of the actual value in an analogous process, for instance by counting the yarn windings. Under certain conditions it could be sufficient to detect the actual value by directly scanning the storage surface by means of a plurality of yarn detectors, preferably at least three yarn detectors, to thereby create near-analogous information for the control unit. The microprocessor in the control unit is charged with an additional function, which however, it is capable of performing without any problem. The winding speed is adjusted in accordance with the desired values in such a manner that at higher winding speed values the size of the yarn supply is reduced at the same rate as the increased speed permits the winding drive mechanism to replenish the yarn supply more rapidly. Also in the case of a reduced consumption rate, the microprocessor acts to ensure that the yarn supply is not undesirably increased.
In one embodiment, a tabular memory stores the desired values in the form of a sequence, which may be of a density practically resulting in a continuous desired-value curve. A reading pointer is adjustable in accordance with the winding speed to read only a respective one of the desired values at any time and to transmit the information derived therefrom to the control unit. For applications of a more simple nature it is also sufficient, however, to provide the desired values at greater intervals, so that only selected winding speed values are concerned, with significant desired-value changes occurring therebetween. In the case of a known mean consumption rate, a single stage may be sufficient, i.e. the then applicable desired value is matched with this consumption rate.
A further alternative embodiment switches from one yarn detector to the next automatically, which results in the associated new desired value becoming effective. The result, however, is a desired-value curve with a number of steps in the course of the curve corresponding to the number of yarn detectors. This is quite sufficient, however, for attaining the desired objective, particularly when there is a great number of such detectors. The spacings between the individual yarn detectors may be individually adjustable. It is thus not necessary to select accurately equal spacings.
If the yarn detector is adjusted in the longitudinal direction of the storage surface in accordance with the winding speed, this adjustment results in a variation of the desired value determining the function of the control unit for the adjustment of the winding speed.
In another embodiment, the desired value is electronically varied by adjusting the limited active detecting section of a wide-band detector. In a simplified form it would even be sufficient to provide a wide-band detector with a longitudinally displaceable shutter opening permitting the location whereat the wide-band detector scans the storage surface to be displaced in response to variations of the winding speed, to thereby vary the desired value.
Association of the desired values to winding speed values selected at uniform intervals is favourable for obtaining a stable control response.
Since the capability of the winding drive mechanism of replenishing the yarn supply more rapidly at higher winding speeds than at lower winding speeds may vary in accordance with the speed in a non-linear proportion, in the range of the lower winding speed values the differences between the desired values may be relatively small. The differences between the desired values are then of course relatively greater at higher winding speed values.
One embodiment includes a particularly simple construction permitting the desired value corresponding to the known mean consumption rate to be applied to the electronic control unit in a particularly simple manner. The desired value can be individually adjusted and is automatically accepted and used by the control unit for maintaining the yarn supply desirably small during normal operation.